If she's going to be using this mainly on the bed, then how much of a cushion does she really need. I mean, is your bed really really really hard? If not, I'd say just leave it as is.

Super job on this. Would love to make one for my cat but with a top and a hole that she could crawl in. You know how cats love claustrophobic places! Ick!!

I'm going to take the advice of my KH friends and just leave it be, no cushion for now. Katie likes to lay on her back and wiggle around, bicycling her legs in the air, I think to scritch her back! So the bottom of this bed, with the felted waves of slight ripped will do the trick!